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A very compact microstrip reconfigurable filter for fourth-generation (4G) and sub-6 GHz fifth-generation (5G) systems using a new hybrid co-simulation method is presented in this manuscript. The basic microstrip design uses three coupled line resonators with λ/4 open-circuited stubs. The coupling coefficients between the adjacent and non-adjacent resonators are used to tune the filter at the required center frequency to cover the frequency range from 2.5 to 3.8 GHz. The coupling coefficient factors between the adjacent resonators are adjusted to control and achieve the required bandwidth, while the input and output external quality factors are adjusted to ensure maximum power transfer between the input and output ports. Two varactor diodes and biasing circuit components are selected and designed to meet the targeted performance for the tunable filter. The impedance bandwidth is maintained between 95 and 115 MHz with measured return losses of more than 17 dB and measured insertion loss of less than 1 dB. Computer simulation technology (CST) is utilized to design and optimize the presented reconfigurable filter, with hybrid co-simulation technique, using both CST microwave studio (MWS) and CST design studio (DS), is applied to build the model by considering the SPICE representation for the varactor switches and all electronic elements of the biasing circuit. The introduced reconfigurable microstrip filter is also fabricated using a Rogers RO3010 material with a relative dielectric constant of 10.1 and it is printed on a very compact size of 13 × 8 × 0.81 mm3. An excellent agreement is obtained between the simulation and measurement performance.

A dual-port transparent multiple-input multiple-output (MIMO) antenna resonating at sub-6 GHz 5G band is proposed by using patch/ground material as transparent conductive oxide (AgHT-8) and a transparent Plexiglas substrate. Two identical circular-shaped radiating elements fed by using a microstrip feedline are designed using the finite element method (FEM) based high-frequency structure simulator (HFSS) software. The effect of the isolation mechanism is discussed using two cases. In case 1, the two horizontally positioned elements are oriented in a similar direction with a separate ground plane, whereas in case 2, the elements are vertically placed facing opposite to each other with an allied ground. In both cases, the transparent antennas span over a −10 dB band of 4.65 to 4.97 GHz (300 MHz) with isolation greater than 15 dB among two elements. The diversity parameters are also analyzed for both the cases covering the correlation coefficient (ECC), mean effective gain (MEG), diversity gain (DG), and channel capacity loss (CCL). The average gain and efficiency above 1 dBi and 45%, respectively with satisfactory MIMO diversity performance, makes the transparent MIMO antenna an appropriate choice for smart IoT devices working in the sub-6 GHz 5G band by mitigating the co-site location and visual clutter issues.

Multiple-input multiple-output (MIMO) antennas with four and eight elements having connected grounds are designed for ultra-wideband applications. Careful optimization of the lines connecting the grounds leads to reduced mutual coupling amongst the radiating patches. The proposed antenna has a modified substrate geometry and comprises a circular arc-shaped conductive element on the top with the modified ground plane geometry. Polarization diversity and isolation are achieved by replicating the elements orthogonally forming a plus shape antenna structure. The modified ground plane consists of an inverted L strip and semi ellipse slot over the partial ground that helps the antenna in achieving effective wide bandwidth spanning from (117.91%) 2.84–11 GHz. Both 4/8-port antenna achieves a size of 0.61 λ × 0.61 λ mm2 (lowest frequency) where 4-port antenna is printed on FR4 substrate. The 4-port UWB MIMO antenna attains wide impedance bandwidth, Omni-directional pattern, isolation >15 dB, ECC < 0.015, and average gain >4.5 dB making the MIMO antenna suitable for portable UWB applications. Four element antenna structure is further extended to 8-element configuration with the connected ground where the decent value of IBW, isolation, and ECC is achieved.

Interconnected three-element and four-element wideband MIMO antennas have been proposed for millimeter-wave 5G applications by performing numerical computations and carrying out experimental measurements. The antenna structure is realized using Rogers 5880 substrate (εr = 2.2, tan δ = 0.0009), where the radiating element has the shape of an inverted L with a partial ground. The unit element is carefully designed and positioned (by orthogonally rotating the elements) to form three-element (case 1) and four-element (case 2) MIMO antennas. The interconnected ground for both cases is ascertained to increase the practical utilization of the resonator. The proposed MIMO antenna size is (0.95λ × 3λ) for case 1 and (2.01λ × 1.95λ) for case 2 (at the lowest functional frequency). Both the designs give an impedance bandwidth of approximately 26–40 GHz (43%). Moreover, they achieve greater than 15 dB isolation and more than 6 dBi gain with an ECC value lower than 0.02, which meets the MIMO diversity performance thus making the three-element and four-element MIMO antennas the best choice for millimeter-wave 5G applications.

This article demonstrates the design and development of WR-15 transition using an antipodal microstrip dipole antenna at a frequency of 60 GHz for space applications. An inline microstrip line to rectangular waveguide (MS-to-RWG) transition is proposed for the V-band (50–75 GHz) functioning. The RF energy is coupled and launched through an antipodal dipole microstrip antenna. Impedance matching and mode matching between the MS line and dipole are achieved by a quarter wave impedance transformer. This results in the better performance of transitions in terms of insertion loss (IL > −0.50 dB) and return loss (RL < −10 dB) for a 40.76% relative bandwidth from 55.57 GHz to 65.76 GHz. The lowest values of IL and RL at 60 GHz are −0.09 dB and −32.05 dB, respectively. A 50 μm thick double-sided etched InP substrate material is used for microstrip antipodal dipole antenna design. A back-to-back designed transition has IL > −0.70 dB and RL < −10 dB from 54.29 GHz to 64.07 GHz. The inline transition design is simple in structure, easy to fabricate, robust, compact, and economic; occupies less space because the transition size is exactly equal to the WR-15 length; and is prepared using an InP substrate with high permittivity of 12.4 and thickness of 50 μm. Thus, the devices have the lowest insertion loss value and lowest return loss (RL) value, of <−31 dB, as compared to earlier designs in the literature. Therefore, the proposed design has the lowest radiation loss (because of thickness) and highest transmission (about 97% power). Easy impedance matching using only a single-step quarter-wave transformer between the antipodal dipole antenna and 50 Ω microstrip line (avoiding the multi-sections’ demand and microstrip line’s tedious complexity) is needed. Since, when the InP dielectric substrate is inserted in WR-15, the waveguide becomes a dielectric-filled waveguide (DFWG), and its characteristics impedance reduces to 143 Ω from 505 Ω at an operating frequency of 60 GHz. In the proposed transition, no ridge waveguide or waveguide back-short is utilized in WR-15. The microstrip line did not contain any via, fence, window, screw, galvanic structure, post, etc. Hence, the transition is suitable for high-data-rate 5G communications, satellite remote sensing, missile navigation, MIC/MMIC circuits’ characterization, and mm-wave applications. The electrical equivalent model of the proposed design has been generated and validated using an RF circuit simulator and was found to have excellent matching.

A printed and minimal size antenna having the functionality of frequency shifting as well as pattern reconfigurability is presented in this work. The antenna proposed in this work consists of three switches. Switch 1 is a lumped switch that controls the operating bands of the antenna. Switch 2 and Switch 3 controls the beam switching of the antenna. When the Switch 1 is ON, the proposed antenna operates at 3.1 GHz and 6.8 GHz, covering the 2.5–4.2 GHz and 6.2–7.4 GHz bands, respectively. When Switch 1 is OFF, the antenna operates only at 3.1 GHz covering the 2.5–4.2 GHz band. The desired beam from the antenna can be obtained by adjusting the ON and OFF states of Switches 2 and 3. Unique beams can be obtained by different combination of ON and OFF states of the Switches 2 and 3. A gain greater than 3.7 dBi is obtained for all four cases.

<p><b>A complete guide to optical&#45;wireless from 5G and beyond</b> <p>The mobile market has experienced unprecedented growth over the last few decades. Consumer trends have shifted towards mobile internet services supported by 3G and 4G networks worldwide. Inherent to existing networks are problems such as lack of spectrum, high energy consumption, and inter&#45;cell interference. These limitations have led to the emergence of 5G technology. It is clear that any 5G system will integrate optical communications, which is already a mainstay of wide area networks. Using an optical core to route 5G data raises significant questions of how wireless and optical can coexist in synergy to provide smooth, end&#45;to&#45;end communication pathways. <i>Optical and Wireless Convergence for 5G Networks</i> explores new emerging technologies, concepts, and approaches for seamlessly integrating optical&#45;wireless for 5G and beyond. <p>Considering both fronthaul and backhaul perspectives, this timely book provides insights on managing an ecosystem of mixed and multiple access network communications focused on optical&#45;wireless convergence. Topics include Fiber&#150;Wireless &#40;FiWi&#41;, Hybrid Fiber&#45;Wireless &#40;HFW&#41;, Visible Light Communication &#40;VLC&#41;, 5G optical sensing technologies, approaches to real&#45;time IoT applications, Tactile Internet, Fog Computing &#40;FC&#41;, Network Functions Virtualization &#40;NFV&#41;, Software&#45;De???ned Networking &#40;SDN&#41;, and many others. This book aims to provide an inclusive survey of 5G optical&#45;wireless requirements, architecture developments, and technological solutions; in particular, this book: <ul> <li>Offers new insights on the highly relevant topic of 5G optical&#45;wireless convergence</li> <li>Guides early&#45;stage researchers by providing a solid platform on which to build future research</li> <li>Helps mobile/optical stakeholders to construct new project proposals that meet challenges associated with 5G and beyond at the international level</li> <li>Includes contributions from international experts at the forefront of 5G research representing industrial and academia stakeholders</li> <li>Presents background information suitable for a range of optical and wireless courses</li> </ul> <p><i>Optical and Wireless Convergence for 5G Networks</i> is an indispensable resource for fixed and mobile stakeholders, wireless industry professionals, graduate students and postdoctoral researchers, and those in related areas of telecommunications and electronic engineering.

The development of low specific absorption rate (SAR) antennas is crucial for safety and efficiency in wireless communication and biomedical applications. This study introduces a low SAR ultra-wideband (UWB) rectangular microstrip monopole antenna with an extended ground plane. The design operates effectively in free space and on a human body phantom. It achieves a reflection coefficient of -42.59 dB at 2.48 GHz and covers the S-band from 2.31 GHz to 4.12 GHz with a peak gain of 5.09 dBi in free space. The antenna maintains consistent performances when placed on a human phantom. With reverse and front patch faces, its gain improves to 5.53 dBi and 5.80 dBi, respectively. Experimental validation of the fabricated prototype shows excellent agreement with simulations conducted using high-frequency structure simulators (HFSS) and advanced design systems (ADS). Additionally, lumped-element equivalent circuits are used to analyze impedance behavior in both environments, confirming the antenna’s robustdesign.  

Future 5G wireless systems will have substantial challenges in integrating the sub-6 GHz and millimeter-wave (mm-wave) bands due to their massive frequency ratios. This paper proposes a machine learning-optimized compact wearable frequency-reconfigurable antenna for sub-6 GHz/mm-wave 5G integration. Fabricated on a flexible Rogers Duroid substrate (27.8 × 14 × 0.508 mm 3 ), the antenna initially employs a circular structure resonating at 28 GHz. Dual-band operation (3.5 GHz and 28 GHz) is achieved by etching an H-shaped slot into the rectangular patch. A PIN diode is employed to reconfigure the proposed antenna in the ON and OFF states. In the ON state, the antenna operates at 3.5 GHz and 28 GHz, achieving measured bandwidths of 25.4% and 73.2%, gains of 3.63 dBi and 5.25 dBi, and radiation efficiencies of 90.5% and 88%, respectively. In the OFF state, the antenna operates at 28 GHz, achieving a measured bandwidth of 72.9%, gain of 6.2 dBi, and a radiation efficiency of 89%. Bidirectional E-plane and omnidirectional H-plane radiation patterns are maintained across both bands. At 3.5 GHz, the specific absorption rate (SAR) value for 1 g and 10 g of human tissue is 0.438 W/kg and 0.0147 W/kg, while at 28 GHz, the SAR value is 0.801 W/kg and 1.09 W/kg, which comply with the FCC and ICNIRP standards. Bending tests (lap, chest, arm) demonstrate stable on-body performance. The antenna’s S 11 was predicted using a supervised ML regression framework. Among tested algorithms, the decision tree achieved state-of-the-art accuracy (R 2 : 97.80%) with minimal errors (MAE: 0.72, MSE: 0.28, MSLE: 0.56, RMSLE: 0.81, RMSE: 0.66). The proposed antenna system is suitable for future 5G devices.

Employing electromagnetic fields (EMFs) in new wireless communication and sensing technologies has substantially increased the level of human exposure to EMF waves. This paper presents a useful insight into the interaction of electromagnetic fields with biological media that is defined by the heat generation due to induced currents and dielectric loss. The specific absorption rate (SAR) defines the heating amount in a biological medium that is irradiated by an electromagnetic field value. The paper reviews the radio frequency hazards due to the SAR based on various safety standards and organisations, including a detailed investigation of previously published work in terms of modelling and measurements. It also summarises the most common techniques utilised between 1978 and 2021, in terms of the operational frequency spectrum, bandwidth, and SAR values.